Transmission line arc detecting and eliminating system wherein the energy source is continually disabled and enabled



March 1, 1966 Filed Feb. 7, 1963 A. J. DE VITA ETAL TRANSMISSION LINEARG DETECTING AND ELIMINATI SYSTEM WHEREIN THE ENERGY SOURCE ISGONTINUALLY DISABLED AND ENABLED 2 Sheets-Sheet 1 @y WMMQM ATTORNEY Muchl, 1966 A. J. D vrrA ETAL ,238,475

TRANSMISSION LINE ARC DETECTING AND ELIMINATING SYSTEM WHEREIN THEENERGY SOURCE IS GONTINUALLY DISABLED AND ENABLED 2 Sheets-Sheet 2 FiledFeb. 7, 1965 NHT FQ QSNH /NVENTOHS ALPHONSEJ DEV/TA ROSSMNG/APA/VE ByM2M l UwO A II ATTORNEY United States Patent O M TRANSMISSION LINE ARCDETECTING AND ELIMINATING SYSTEM WHEREHN THE EN- ERGY SQURCE ISCONTNUALLY DISABLED AND ENABLED Alphonse J. De Vita, Chelmsford, andRosario Mangiapane, Burlington, Mass., assignors to Raytheon Company,Lexington, Mass., a corporation of Delaware Filed Feb. 7, 1963, Ser. No.256,857 14 Claims. (Cl. S33-17) This invention relates to high powerradiation systems and, more particularly, to arrangements for detectingvoltage breakdown arcs and purging the cause of said arcs which oftenoccur in such systems.

One of the major problems incident to the operation of high powermicrowave systems, and particularly high power continuous wavetransmitters or microwave generators, resides in the fact that aftervoltage breakdown arcs form, they often walk in the interior of theoutput waveguide circuits towards the microwave generator which is usedto provide energy to said output waveguide circuit. Even though thepower normally employed in the system may be much lower than the nominalbreakdown value for the waveguide employed, local conditions such as theappearance of some lossy foreign matter in the guide will raise thetemperature of the air in the guide to its breakdown voltage, therebycausing arcing. Generally speaking, an arc initiated anywhere in acontinuous wave system, if not extinguished, will walk back along thewaveguide toward the microwave generator, such as a magnetron or othertube generator having an evacuated interior and a window, and destroy orburn the generator window. Furthermore, the speed of travel of the arcis a function of power applied by the microwave tube generator and,therefore, for high power continuous wave systems providing outputpowers greater than one kilowatt, some sort of arc detection andcleansing of dirt or lossy material is required, particularly in fieldoperations where lthere is a tendency for dirt to enter and accumulatein the interior of the output waveguide circuits. Systems availabletoday primarily rely on the shutting olf of the microwave tube generatorafter the detection of the presence of an arc and then cleaning thewaveguide by blowing air through the waveguide to blow out the dirt orlossy material so as to preclude the reinitiation of au arc uponreturning the microwave generator to full power. Furthermore, the arcdetection and suppression systems available today do not providecomplete protection of the microwave tube output window due to theirinability to recognize an arc without intercepting the arc.

Therefore, it is an object of the present invention to eliminate damageto high powered generators such as may be caused by the existence ofvoltage breakdown arcs.

It is an additional object to provide a system which purges the cause ofthe initiation of a voltage breakdown arc in the output waveguidecircuits coupled to an energy generator.

In accordance with this invention, means are provided for detecting thepresence of an arc within a transmission medium such as air or in atransmission line as a waveguide and purging the cause of the initiationof the arc before damage can be done to a generator supplyingelectromagnetic energy to said medium or transmission line. For thispurpose, a plurality of energyk detectors or sensors are positioned suchthat the presence of an arc in the transmission line will be detecteddue to the reduction in power caused by the energy absorption andreflection of the arc. A detection device responsive to the unequalenergy intercepted by said sensors in the presence of an arc in saidwaveguide provides a signal to actuate 3,238,475 Patented Mar. 1, 1966 acontrol circuit. The control circuit provides an output signal to reducethe power being provided to the transmission line. The control circuitfurther operates in such a manner as to provide means for thetransmission line to purge itself of the lossy material causing thearcing. Additionally, a probe arc detection system is arranged incombination with the above-mentioned t0 provide a self-purging arcdetection system in combination with a probe arc detection system.

Other objectives and features of this invention will become apparentfrom the following description taken in conjunction with the followingdrawings wherein:

FIG. l is a schematic diagram of a self-purging arc detection systemincluding a microwave generator, waveguide, and sensors and detectionand control circuitry according to the invention; and K FIG. 2 is aschematic diagram of a self-purging arc detection system in combinationwith a probe arc detection system.

Referring now to FIG. l, which shows a self-purging arc detection systemincluding an energy generator, a rectangular waveguide circuit, and apair of detectors or sensors in combination with detection and controlcircuitry according to the invention. High frequency oscillator 1l),such as a klystron, is shown for providing an actuating high frequencymicrowave signal through a waveguide circuit 11 and an isolator 12 tothe high power output section of the system. Isolator 12 providesisolation of the oscillator 10 from high power amplier 16 of the system.Isolator 12 is a ferrite isolator which operates on the gyromagneticresonance principle and provides isolation by absorption of reflectedenergy. The energy then flows from the isolator through the waveguide 13to a power switch 14, which could be of the ferrite, ferroelectric orother types. The ferrite switch 14 shown herein is used to control theflow of energy from the high frequency oscillator 10 to the high poweramplifier 16 of the system. The ferrite switch operates on the faradayrotation principle. In response to an actuating signal applied to switch14 a 90 rotation is imparted to the E vector of the energy being appliedfrom waveguide 13. In the absence of a signal being applied to theswitch 14, a 0 rotation is obtained and approximately all of the powerprovided by waveguide 13 is reflected and absorbed by isolator 12. Withferrite switch 14 in the energized condition, energy from the highfrequency oscillator 10 will flow through the waveguide 15, to drivehigh power amplifier 16. Waveguide 15 is positioned orthogonal towaveguide 13 and is coupled to switch 14, thus providing a reflectivemismatch condition between waveguides 13 and 15 in the absence of anactuating signal being applied to switch 14. High power amplifier 16could be of the klystron, magnetron or other high power energy generatortypes. The power amplifier 16 which is shown herein as an evacuated tubeis shown having an output section or port 17 with a transparent window18 for permitting energy generated by the power amplifier to be forwardcoupled to an output waveguide circuit 20. The transparent window 18could be of a dielectric material, such as ceramic, which is transparentto microwave energy. Power amplier 16 is also provided with a waveguidecoupling section 21 which is shown coupled to the output port 17 andpositioned so as to extract and sample a portion of the forward coupledor transmitted energy prior to the passing of such energy through thetransparent window 1S. Coupler 21 is connected to the output port 17through a plurality of dielectric window filled waveguide orices 23,which are incorporated in the wall of the waveguide and are of suicientdiameter at the operating frequency to permit a small portion of theenergy to be sampled or extracted from the energy passing through theoutput port. The

energy entering the coupler section 21 is then attenuated by anattenuating device 32 which is of a microwave absorbent material, suchas a carbon material, and is shown with an adjustable arm 24 forcontrolling the amount of attenuation. The attenuation is controlled byadjusting attenuating device 32 so that it intercepts a great amount ofthe energy section as shown herein. The power thus sampled is detectedby a microwave detector or sensor, such as a microwave rectifier 25,inserted across the coupler 21 having an output terminal 26. Themicrowave detector is inserted through the top and bottom wall portionsof the coupler so as to detect the sampled power from power amplifier16. In this instance, detector 25 is of that type of microwave rectifierwhich produces a negative voltage signal at its output terminal 26 uponthe interception of microwave energy, and is designated as the ER typeof microwave detector, by the microwave industry.

The forward coupled microwave power from high frequency power amplifier16 passes from port 17 through transparent window 1S to output waveguidecircuit 20 and is shown, in this instance, as coupled to a load such asan antenna 27 by way of a waveguide output coupler 28. Positioned alongthe length of the waveguide in proximity to the load 27, a secondcoupler is shown physically connected to waveguide 20 to extract andsample a portion of the energy passing through the waveguide 2t) whichis being supplied to the load 27. The coupler 29 is physically connectedto waveguide 2t? by way of a plurality of orifices 33 of a size such asdescribed in connection with coupler 21 which permit the forward coupledpower to be sampled and detected by a microwave detector 3G, such as amicrowave rectifier, having an output terminal 31. Microwave detector 30is shown in FIG. l as being inserted into coupler 29, similarly asdescribed in relation to detector 25, so as to rectify the sampledmicrowave power and produce an output signal at terminal 31. In thisinstance, microwave detector 30 is of the E type, as known by themicrowave industry, and provides a positive output signal at terminal 31in the presence of detectable microwave energy in the proximity of load27.

During normal operation of the system, high power microwave energy isbeing supplied to the output waveguide circuit from the power amplifier16. For purposes of explanation, assume that during operation of thesystern, a piece of lossy foreign matter 70, such as dust, enters anddeposits itself in the waveguide somewhere between the sampling orifices23 and 33 which supply sampled forward coupled microwave energy tomicrowave detectors and 30, respectively. The presence of this lossyforeign material '76 in the waveguide will absorb energy passing throughthe waveguide and become heated. This heating, by way of the absorptionof energy, will cause the air temperature present in the waveguide 20 inthe vicinity of the foreign material to be raised to its breakdownvoltage. When the air, in proximity to particle 7d, reaches itsbreakdown voltage, an arc will be formed within waveguide 2l. It hasbeen experimentally observed that when an arc discharge occurs within awaveguide, the arc formed will dissipate or absorb approximately 75percent of the power incident to the arc and will reflect the remainderof the energy towards the `generator 16. The absorption percentage ofthe arc is variable and is dependent on the microwave energy power levelin the waveguide, the waveguide size, the temperature, and the airpressure within the waveguide.

Once struck across the guide 20, an arc will travel toward the microwavepower source 16 and will, if not impeded, impinge on the dielectricwindow 18. The arc will continue to dissipate and absorb microwaveenergy until it punctures either the ceramic window or the sealsurrounding the ceramic window and thus destroys the power amplifier 16.Due to this characteristic of energy f-iabsorption by an arc, it ispossible to sense the difference in forward coupled transmitted energythrough waveguide 20 by detectors 25 and 30, and thus prevent damage andultimate destruction of power amplifier 16.

Referring again to FIG. 1, there is shown an unbalance detection circuit40 Connected to detectors 25 and 3d at terminals 26 and 31 so thatdifferences in sampled microwave energy levels, caused by the presenceof an arc in the waveguide 20 can be detected. In the absence of arcingin waveguide 2t), detector 3@ provides a positive output voltage inresponse to sampled microwave energy, but due to the initiation ofarcing in the waveguide circuit 2t) and the subsequent absorption ofmicrowave energy by the arc, the positive output voltage signal providedby`detector 3f) will drop towards a zero voltage level. Thus, by sensingthe difference between the negative output voltage at terminal 26 ofdetector 25 and the normally positive voltage at terminal 31 of detector30, it is possible using unbalancing or nulling circuits to detect thepresence of an arc in the waveguide In this instance, terminal 26 ofdetector 25 and terminal 31 of detector 30 are connected across anulling circuit comprising resistors 41, ft2, 43, and 44. Arcing in thewaveguide causes the nulling circuit to produce a negative going outputsignal. The nulling circuit sums the voltages produced by the sensorsand provides a signal to actuate duotriode 45, upon the sensing of anarc in waveguide circuit 20. Duotriode 45 has one section with a cathode46, grid 47 and plate 48 which henceforth will be referred to as sectionA and another section having a cathode 56, grid 57 and a plate '58 whichhenceforth will be referred to as section B. Cathodes 46 and 56 areconnected together and are biased negative through a resistor 49 by abattery 5t). Grid 47 of section A is connected to respond to voltagesignal changes provided by the nulling circuit, comprising resistors 41,d2, 43, and 4d. Grid 57 is connected to ground. Plate 4S is connectedthrough a load resistor 51 to a B+ voltage source 52 and is alsoconnected through output voltage dividing resistors 53 and 54 to biasingvoltage source 55. Plate 58 is connected through a load resistor 59 to aB-lvoltage source 60. Additionally, plate 58 is connected throughvoltage divider resistors 61 and 62 to a biasing voltage source 63.Normally, both sections A and B of the duotriode are in the on orconducting condition since grids 47 and 57 are normally biased at zeropotential. Therefore, plates 48 and 58 of the duotriode sections A and Bare normally above ground but quiesced somewhere below the voltagesource potential of 52 and 60, respectively.

In response to the detection of an arc in the waveguide Ztl, a negativesignal will be applied from the nulling circuit to the grid 47 ofsection A. Plate 48 will then become more positive due to theapplication of the negative voltage to grid 47 driving duotriode sectionA towards cutoff. Therefore, a positive voltage will appear at theintersection of divider resistors 53 and 54 and will cause a positiveactuating signal to be applied to turn on thyratron 71. Thyratron 71comprises a plate 72, grid 73, second grid 74, and a cathode 75. Grid'74 is connected to input resistor 78, plate 72 is connected through aload resistor 76 to an alternating source of voltage 77, such as a 400cycle A.C. supply voltage, and

r grid 73 is directly connected to ground and cathode 75 is connectedthrough an output cathode resistor y94 to ground.

Additionally, a second thyratron 80 is shown as a part of unbalancedetection circuit 40 having a plate S1, a first grid 82, a second grid83 and a cathode 84. The grid 83 is connected through input resistor tothe junction of dividing resistors 61 and 62. Plate 81 is connectedthrough a load resistor S5 to an alternating source of voltage 86, suchas a 400 cycle alternating supply voltage. Grid 82 is connected toground and cathode 84 is connected to the junction of cathode 75 andoutlput resistor 94.

The application of the positive signal from the divider resistor network53 and 54 to the grid 73 allows thyratron 71 to be turned on uponapplication of the next positive voltage cycle from voltage source 77 toplate 72. Therefore, on the next positive cycle of alternating voltagefrom voltage source 77, thyratron 71 will turn on in the conventionalmanner and produce a positive signal output across resistor 94 andground. This output signal is then applied to actuate control circuit88. Thyratrons 71 and 80 are used to provide an actuating signal to acircuit which controls the energy being applied to waveguide circuit 20.Section B of duotriode 45 is shown adapted to detect a failure ofdetector 25. The failure of detector 25 will cause a positive signal tobe applied through the nulling circuit to the grid 47 of section A ofduotriode 45. This will cause the duotriode section A, comprisingcathode 46, grid 47 and plate 48 to conduct more heavily and thus thesection B, comprising cathode 56, grid 57 and plate 58 will not conductas fully, therefore, producing a positive signal at the plate 58. Thispositive signal at the plate 5S is then applied through dividerresistors 61 and 62 and input resistor 87 to grid 82. Thyratron 80 thenconducts on the next positive half cycle applied to plate 81 byalternating voltage source 86 in the same manner as described withrelation to thyratron 71. Due to the initiation conduction of thyratron80, a positive going output signal is then provided across resistor 94,which then can be used to actuate a switch control circuit 88.Thyratrons 71 and 30 both turn off in the conventional manner uponapplication of the negative voltage cycle being applied to plates 72 and81 from 400 cycle voltage sources 77 and 06, respectively.

The positive output signal provided by unbalance detection circuit 40across resistor 94 in the event of an arc in the waveguide or of afailure in detectors 25 and 30 is transmitted to actuate switch controlcircuit 8S. Control circuit S8 comprises a lirst controlled rectifier 90having an anode 91, cathode 92 and a gate 93. Control rectifier 90provides a negative pulse to the anode and gate of a controlledrectifier 120, which causes controlled rectifier 120 to extinguish andremain extinguished for a predetermined period of time. Cathode 92 isconnected to ground and gate 93 is connected to the output load resistor94 of unbalance circuit 40. Anode 91 is connected through a loadresistor 99 to a biasing voltage source 100. A clamping circuitcomprising series connected resistors 96 and 97 is connected to avoltage source 98 and is shown connected at the junction of resistors 96and 97 through a clamping diode 95 t0 anode 91.

A transistor 101 of the N-P-N type is shown having a collector 102, abase 103 and an emitter 104. Collector 102 is shown connected through aload resistor 105 toa voltage source 106. The base 103 is shownconnected to the anode 91 of controlled rectifier 90 and through aswitching diode 107 to the emitter 104. The emitter 104 is connectedthrough an emitter circuit charging capacitor 108 .andan emitterresistor 109 to ground. Additionally, emitter 104 is connected throughanother emitter charging capacitor 110 `and resistor 111 to ground.

A sec-ond controlled rectifier 120 having an anode 121, cathode 122 anda gate 123 is shown. Anode 121 is shown connected through output dividerload resistors 124 and 125 to a voltage source 126. Cathode 122 is:shown connected to ground; the gate 123 lis shown connected through acharging capacitor 115 to ground and through a biasing resistor 116 to asource of biasing voltage 117. Additionally, gate 123 is shown connectedthrough a switching diode 113 to the junction of capacitor 108 andresistor 109. Furthermore, anode 121 is shown connected through anisolating diode 112 to the junction of capacitor 110 and resistor 111.

In the absence of an .arc in waveguide 20, no input signal will appearacross output resistor 94 of the unbalance detection circuit 40,therefore, because of biasing, controlled rectifier and transistor 101will be in the off condition and controlled rectifier 120 will be in theon condition. Capacitors 108 and 110 will be charged positively on thesides connected to emitter 104 of transistor 101. The capacitors 108 and110 are charged positive-ly by transistor 101 conducting for .a shorttime after the initial connection of voltage sources and 106 and is thencut off yas its emitter 104 becomes more positive than its base 103. Theconduction of controlled rectifier 120 causes `a current to flow throughresistor 124 and produce a voltage drop ac-ross resistor 124, which isused to maintain ferrite switch 14 in the on condi-tion, thus permittingmicrowave actuating energy from oscillator 10 to energize high frequencypower amplifier 16. Upon the sensing of an arc -in waveguide 20, apositive output voltage will appear across resistor 94 and be applied tothe gate 93 to turn on controlled rectifier 90. The turning on ofcontrolled rectifier 90 produces a negative signal -at anode 91 which isapplied through an isolating diode 107, capacitor and an isolating diode112 to anode 121 of controlled rectifier 120. Additionally, this4negative signal at the lanode 91 `of controlled rectifier 90 issimultaneously applied through diode 107, capacitor 108, -an isolatingdiode 113 to gate 123 of -controlled rectifier 120. The application ofthis negative potential .to the vanode 121 of controlled rectifier 120turns off controlled rectifier 120, thus causing switch 14 to be placedin the off condition. Switch 14 will no longer permit high frequencyactuating energy to be applied to keep high frequency power amplifier 16in the on condition. Therefore, there will no longe-r be provided a.source of forward coupled microwave power to the output waveguidecircuit 20 to sustain the arc. Additionally, the simultaneously negativepulse applied to the gate 123 will charge capacitor 115 to a 4negativepotential so that controlled rectifier 120 will not turn on once againuntil capacitor 115 discharges through resistor 116. When controlledrectier 120 once again initiates conduction, switch 14 is placed in theon condition by voltage developed across resistor 124 so as to fainceagain permit power to be generated by power ampli- After controlledrectifier 90 is turned on by the :positive pulse yat its gate 93, itwill conduct for a short predetermined period ot` time. Thispredetermined time lis less than the time it takes for capacitor todischarge through :resistor 116 to turn on controlled rectifier 120 -toset up the circuit in :a ready condition to turn off rectifier should anarc occur. The c-ontrolled rectifier 90 as shown in FIG. l is biased inits anode circuit in a starved condition. This starved condition isbrought about by the fact that resistor 99 is of such Ka magnitude thatit will not allow sufiicient current to fiow from voltage source 100 tosustain conduction of controlled rectifier 90. Therefore, in order tosustain controlled rectifier 90 for a `short period of time .so thatturning on of controlled rect-ifier 90 will take place, capacitors 110and 108 discharge through diode 107 and provide sufcient current for alimited period of time, determined by the time constant of the-irdischarge, :so Kas to sustain conduction of controlled rectifier 90.After the capacitors 108 .and 110 have discharged, controlled rectifier90 will turn off, inasmuch as the current being provided from voltagesource 100 through load resistor 99 can no longer sustain conduction.Transistor 101 will then turn on due to its emitter 104 becoming lmorenegative than its base 103, and thus positively recharge capacitors 10Sand 110 at their ends connected to emitter 104.

Summarizing the operation of control circuit 88, controlled rectifier 90lis turned on by a positive pulse being applied to its gate 93 and thusprovides a negative pulse to the gate and anode circuits of controlledrectifier 120 to turn off controlled rectifier 120. After capacitors 108and 110 have discharged, controlled rectifier 90 will turn off .andtransistor 161 will turn on to recharge capacitors 108 and 110.Controlled rectifier 1211 will then turn on after capacitor 115 hasdischarged through -resistor 116. The turn-ing on of cont-rolledrectifier 12'@ causes current to `flow through resistor 124 and thusprovide a signal to place switch 1li in the on position so as to permitenergy from oscillator 1@ to reinitiate operation of power amplifier 16.Thus, it is seen that controlled rectifier 919 due to thesequence ofoperation, is in a recycled state such that is capable of immediatelyturning controlled rectifier 12@ off again and hence, the output power,should an arc occur in waveguide 2t).

Upon reactivation of power amplifier 16, forward coupled microwaveenergy may once again initiate an arc in the waveguide due to some partof the lossy material which was not completely oxidized remaining in thewaveguide. It is to be noted that lossy material will graduallydissipate itself due to normal oxidizing caused by microwave energyabsorption of the lossy material. If upon reinitiation of the arc, whichin this instance should take a longer period of time due to the smalleramount of lossy foreign matter remaining in the waveguide, detectitoncircuit d and control circuit 88 will once again turn off poweramplifier 16. This turning on and off operation will continue until thelossy material is oxidized to the point where it no long is capable ofinitiating an arc. This continuous turning on and off operaiton providesthe self purging feature in this system. The term self purging is givenfor this oxidation of the lossy Inate rial, inasmuch as it can `be seent-hat with this system there is no requirement that the system be shutdown after arcing takes place in order to clean out the waveguide by anexternal means such as a vacuum cleaner. It can also be seen that withthis system, due to the lossy material being gradually oxidized, theaverage power supplied to the load will increase exponentially in timesince it takes longer each time for the arc to reestablish itself. Thus,the power amplifier 16 will remain on for greater and greater periods oftime until lossy material 70 is burned out or oxidized, therebyexponentially increasing the average output power supplied to the load.It is to be noted that detector provides in effect a reference voltage,the reference voltage being a measure 4of microwave energy being forwardcoupled to the waveguide -circuit 20.

Referring now to FIG. 2, there is shown the combination of a sel-fpurging arc detection system and a waveguide probe arc detection system.The self purging arc detection system is similar to the arc detectionsystem shown and described in relation to FIG. l. More particularly, theunbalance detection circuit MP and the switch control 88 of FIG. l areshown in block diagram form, and the rst coupler 21 is shown physicallypositioned along the waveguide circuit 2t) external to the tube. CouplerZ1 samples forward coupled microwave power provided from the high poweramplier 16 to the waveguide 20 in the same manner as described withrelation to coupler of FIG. l. The coupler 21, with the detector 25inserted therein, is mounted on the waveguide to provide a self purgingarc detection system when power monitoring within the power amplifier 16is not desirable.

The self purging arc detection system as shown in FIG. 2 operates Iinthe same manner as described with relation to the circuitry shown inFIG. 1 except that sensors 2.5 and 31 are mounted on waveguide 20 sothat there is a possibility of an arc being formed between thetransparent window 1S of the port 17 and the first coupler 21, whichcould conceivably destroy the transparent window 18. There-fore, inorder to protect the waveguide Window and to sense the presence of anarc between the transparent window 18 and the coupler 21, a separate arcdetection circuit is provided which has a probe mounted to protectagainst arcs which might occur 'between the coupler 21 and thetransparent window 18.

Probe 130 is shown inserted in the waveguide and preferably isphysically positioned by splitting the small dimension of the waveguide2t) and is perpendicular to the small dimension wall to insure minimuminterference with the transmission of microwave energy from the highpower amplifier 16. The operation of the probe arc detector takesadvantage of the fact that when a microwave arc comes -in contact withan electrode which is negatively charged, it will draw electron currentfrom that electrode. The impedance of arcs in waveguides have beenobserved to vary with the amount of power sustaining the arcs and is afunction of the power being supplied to the system by the high poweramplifier 16. By using a high impedance probe of a value much greaterthan the impedance of any arc which is expected to occur within thewaveguide, it is possible to measure the loading effect of an arc on theprobe, so as to provide a control signal to shut off the power amplifierand thus extinguish the arc. Incorporation of the probe detector and aprobe arc detector circuit 132 with the couplers 21 and 29 permitsoverall arc detection capability, even when sensing within the poweramplifier is not feasible.

High impedance probe 131) is shown with a terminal 131 which isconnected across a voltage divider network in probe are detectioncircuit 132 and comprises a divider resistor 133 which is connected to a`biasing voltage source 134, a `resistor 135, and a combination dividercircuit comprising a bypass capacitor 137, a pair of resistors 136 and138, a source of biasing voltage 142, a resistor 139, a resistor 141,and a diode 141). Probe terminal 131 is connected between the junctionof resistors and 133 and is at a negative potential due to the action ofthe divider network.

Assume, for purposes of explanation, that during the operation of poweramplifier 16, a lossy material 200 somehow ent-ers the waveguide 2t) anddeposits itself 'between the transparent window 18 and the coupler 21.After a period `of time the material by absorption of energy will beginto oxidize and heat up the air in its immediate vicinity, and thus atthe power levels provided by high power amplifier 16, produce an arewhich will creep towards the transparent window 18. Due to the positionof the negatively charged high impedance probe 130, the `arc will comein Contact with the probe and will draw current from the probe. Thecombination divider circuit acts as a clamp device s-o `as not to allowjunction of resistors 136 and 135 to become too positive. This loadingdown of the high impedance probe will effectively short out the dividernetwork, and thus the intersection of resistors 135 and 136, which wasinitially at a negative potential will go positive, thus causing apositive pulse to be applied through input resistor 143 tot turn onthyratron 150. Thyratron is initially in the off condition due to anegative biasing potential applied to grid 153 via the resistor 143which is connected to the junction of resistors 135 and 136. Thyratron150 is shown having a cathode 151, a first grid 152, a second grid 153and `a plate 154. Grid 152 is shown connected to the input resistor 143;plate 154 is shown connected through a load resistor 156 to a voltagenetwork comprising a charging capacitor 155, a resistor 157 and avoltage source 161. Grid 153 is connected across a biasing networkcomprising a biasing resistor 158 connected between the grid 152 and thejunction of resistors 156 and 157 and through a biasing resistor 159 toa source of biasing voltage 160. The biasing network adjusts the tuningpotential of thyratron 150 to a predetermined level. Cathode 151 isshown connected to the input circuit of the switch control circuit 83,`and provides a positive going signal to actuate the control circuit toinsure that the window 18 of the high power amplifier will be protected.Therefore, upon the detection of an arc by probe 130, a positive signalwill be applied via input resistor 143 to turn on normally off thyratron1511 and thereby cause a positive signal to be applied via cathode 151to actuate the switch control circuit 88. Discharging of capacitor turnsoff the thyratron 150 so that the circuit is ready for the nextactuating signal. The switch control circuit 88 functions in the samemanner as described in relation to the description given in FIG. l.

Other embodiments of the invention utilizing the technique `as describedwith relation to the systems shown in FIGS. l and 2 can be employed andmay vary in accordance with the application to be made of the invention.-For example, it would be possible to provide a switch control circuitwhich would turn off the direct current power provided to the high poweramplifier 16 in the presence of an arc. It is to be noted that the useof such a system would operate much slower and provide less protectionthan the embodiments shown in FIGS. 1 and 2. Accordingly, it is desiredthat this invention not be limited except as defined by the `appendedclaims.

What is claimed is:

l. An arc eliminating system including a source of energy and atransmission line circuit associated therewith, means for detecting anarc in said transmission line circuit comprising a pair of microwaveenergy sensors one of said pair operative to sense the energy providedto an input of said transmission line circuit and the other of said pairoperative to sense power supplied to `an output device coupled to saidtransmission line circuit, and arc purging means coupled to saiddetecting 4means and being responsive to the difference in energy insaid pair of sensors for eliminating the cause of said arc bycontinually disabling and enabling said energy source until the cause ofsaid arc is removed. y

2. In a system including a source of energy and `a transmission linecircuit associated therewith, means for detecting a voltage breakdownarc in said transmission line circuit comprising a plurality of energysensors to distinguish between the magnitude of the energy on eitherside of said arc, yand means for disabling said source of energy inresponse to said energy sensors distinguishing between the magnitude ofthe energy on either side of said arc, said means for disablingincluding a means for purging the cause of the initiation of a voltagebreakdown arc in said transmission line circuit by continually disablingand enabling said energy source until said cause is removed.

3. In a system including a source of microwave energy and a transmissionline circuit associated therewith, means for detecting a voltagebreakdown arc in said transmission line circuit comprising 4a pluralityof energy sensors to distinguish between the magnitude of the energy oneither side of said arc, means for disabling said source of energy inresponse to energy sensors distinguishing between the magnitude of theenergy on either side of said arc, said means `for disabling including ameans for purging the cause of the initiation of a voltage breakdown arcin said transmission line circuit by continually disabling and enablingsaid energy source until said `cause is removed, said means fordetecting a voltage breakdown arc having at least one of said sensorspositioned to sense the energy within the source of energy prior to thetransmission of said energy to said transmission line circuit.

4. In a high power microwave system including a source of microwaveenergy providing forward coupled microwave energy to a waveguide outputcircuit associated therewith, means for detecting the existence ofvoltage breakdown arcs in said waveguide comprising a plurality ofenergy sensors positioned to sample forward coupled microwave powerwithin said waveguide, means responsive to a signal provided by saidenergy sensors to provide an output signal to a control circuit, saidcontrol circuit comprising a plurality of controlled rectierscooperating to provide a signal to reduce the amount of energy beingprovided by said power amplier to said waveguide output circuit, andsaid control circuit additionally including means for permitting saidwaveguide output circuit to automatically purge itself of the cause ofthe initiation of said arcs in said output waveguide circuit.

5. In an arc detection system including a source of energy and awaveguide circuit associated therewith, means for sensing the presen-ceof an arc within said waveguide circuit, said means for sensingcomprising a plurality of microwave energy sensors, at least one of saidmicrowave energy sensors positioned so as to internally sample a portionof the microwave energy being supplied from said microwave source tosaid waveguide circuit, means responsive to the energy intercepted bysaid microwave detectors and connected in circuit with said 4microwavesensors, a control circuit responsive to said circuit resp-onsive to thesensing of microwave energy, said control circuit providing microwaveenergy to said output waveguide circuit, and said control circuitproviding means for periodically disabling said microwave source uponreinitiation of an arc in said waveguide circuit until arcing in saidwaveguide circuit can no longer be initiated.

6. A combination sensor and probe arc detection systern including asource of microwave energy and wav-eguide circuit 'associated therewith,means for .sensing the presence of an arc within said waveguide circuit,means for intercepting an arc within said waveguide circuit coactingwith said means for sensing the presence of an arc in said waveguide,said sensor and said probe both independently providing an actuatingsignal to permit disabling of said source of energy if arcing isinitiated within said waveguide circuit, and control circuit meansresponsive to said actuating signal for disabling said microwave energysource upon detection of an arc and periodically disabling saidmicrowave energy source upon reinitiation of said arc in said waveguidecircuit until arcing in said waveguide circuit can n-o longer beinitiated.

7. In an arc detection system including a source of energy and awaveguide -circuit associated therewith, means for sensing the presenceof an arc within said waveguide circuit, said means for sensingcomprising a probe for intercepting an arc within said waveguidecircuit, a control cir-cuit responsive to the interception of said arcby lsaid negatively charged probe for providing an output signal todisable said source of energy, and said control circuit providing meansfor periodi-cally disabling said energy source upon reinitiation of anarc in said waveguide circuit until arcing in said waveguide circuit canno longer be initiated.

8. In a system including a source of energy and an energy transmissionline circuit associated therewith, means for detecting a voltagebreakdown arc in said transmission line circuit comprising a probemounted in said transmission line circuit to intercept a voltagebreakdown arc, said probe being of a relatively high impedance incomparison with the magnitude of the impedance of said arcs expectedwithin said transmission line circuit at the energy levels present insaid transmission line circuit, and control means for detecting theloading of said pro'be by said arc and for continually disabling andenabling said source of energy until the cause of Isaid arc is removed.

9. A system -comprising a source of energy, a transmission line circuitassociated therewith, and means for detecting ion and electron densitiesin a voltage breakdown arc within said transmission line circuitcomprising a probe mounted in said transmission line circuit tointercept said voltage breakdown arc, said probe comprising a negativelycharged electrode from which current is drawn by said arc, and controlmeans for detecting the loading of said probe by said arc and forcontinually disabling and enabling said source of energy until the causeof said arc is removed 10. In a system for measuring ion and electrondensities of a plasma arc occurring within a power transmission linecircuit being fed by a source comprising a probe mounted in atransmission line circuit to intercept a voltage breakdown arc, saidprobe comprising a negatively charged electrode from which current isdrawn by said arc, and said probe being of la relatively high impedancein comparison with the magnitude of the impedances of said arc at `thepower levels expected within said transmission line cir-cuit, andcontrol means for detecting the loading of said probe by said arc andfor continually disabling and enabling said source until the cause ofsaid arc is removed.

11. In an arc detection system .including a source of energy and anoutput waveguide circuit associated therewith, an energy sensor locatedin proximity to the terminus of said output waveguide circuit, saidenergy sensor providing a signal `indicative of the amount of microwaveenergy flowing in the vicinity of said terminus of said output waveguidecircuit whereby an arc can be detected in said output waveguide circuit,a comparison circuit for comparing said output signal of said energysensor with a reference signal, said reference signal being indicativeof the energy which would be flowing within said transmission linecircuit in the absence of an arc in said transmission line circuit, andmeans for disabling said energy source in the presence of an arc withinsaid waveguide circuit, said means for disabling responsive to thecomparison of said signal from said energy sensor and said reference.

12. In a high power microwave arc detect-ion system including a sourceof microwave energy providing forward coupled microwave energy to awaveguide output circuit associated therewith, means for detecting theexistence of voltage breakdown arcs in said waveguide caused by thepresence of a lossy material in said waveguide, comprising a pluralityof microwave energy sensors positioned to sample forward coupledmicrowave power, control means responsive to the detection of microwavebreakdown arcs by said microwave energy sensors, said con-trol meansprovid-ing a signal to reduce the amount of forward coupled microwaveenergy being provided to said waveguide output circuit, and said controlmeans comprising means for periodically reducing the amount of microwaveenergy being provided to the waveguide output circuit until the lossymaterial present in said vol-tage breakdown arc can no longer initiatean arc.

13. In a system including a source of energy and a transmission linecircuit associated therewith, means for detecting a voltage breakdownarc in said transmission line circuit comprising a plurality of energysensors positioned in circuit with said transmission line circuit todistinguish between the magnitude of the energy on either side of saidarc, said energy sensors providing an output signal indicative of theamount of energy sensed, means for nulling in response to said sensorou-tput signals, means for :sampling a signal provided by said means fornulling, control means responsive to said sampling means for reducingthe energy provided by said source of energy to said -transmission linecircuit, said control means including means to prepare said controlmeans for the possible reinitiation of an arc in said transmission linecircuit prior to said control means returning said source of energy tofull power.

14. In a system including a source of energy and a transmission linecircuit associated therewith, means for detecting voltage breakdownarcing in said transmission line circuit comprising a plurality ofrectifying energy sensors positioned in circuit with said transmissionline circuit to distinguish between the magnitude of the energy oneither side of said arcing, said rectifying sensors pro* viding anoutput signal indicative of the magnitude of energy sensed, an unbalancecircuit responsive to said output signals provided by said plurality ofenergy sensors, controlled electrical discharge means in circuit withsaid unbalance circuit and responsive to said unbalance circuit forcyclically sampling an output signal from said unbalance circuit,con-trol means responsive and in circuit with said electronic dischargemeans for disabling said soure of energy upon the reinitiation of an arcformed within said transmission line circuit, said control meanscomprising means for permitting said transmission line circuit :to bepurged of the lossy materal causing initia- Ition 4of said arcing.

References Cited by the Examiner UNITED STATES PATENTS 1,896,856 2/1933Traver 317-42 2,344,261 3/1944 Mortlock 317-44 2,493,720 2/1950 Wild331-62 2,498,719 2/1950 Spencer 331-62 2,557,180 6/1951 Fiske 333-982,860,244 11/1958 Crowley 3 25-150 3,028,507 4/1962 Sacks 307-8853,081,438 3/1963 Levy 1533-242 HERMAN KARL SAALBACH, Prz'maly Examiner.

W'. K. TAYLOR, P. L. GENSLER, Assistant Examiners.

2. IN A SYSTEM INCLUDING A SOURCE OF ENERGY AND A TRANSMISSION LINECIRCUIT ASSOCIATED THEREWITH, MEANS FOR DETECTING A VOALTAGE BREAKDOWNARC IN SAID TRANSMISSION LINE CICRUIT COMPRISING A PLURALITY OF ENERGYSENSORS TO DISTINGUISH BETWEEN THE MAGNITUDE OF THE ENERGY ON EITHERSIDE OF SAID ARC, AND MEANS FOR DISABLING SAID SOURCE OF ENERGY INRESPONSE TO SAID ENERGY SENSORS DISTINGUISHING BETWEEN THE MAGNITUDE OFTHE ENERGY ON EITHER SIDE OF SAID ARC, SAID MEANS FOR DISABLINGINCLUDING A MEANS FOR PURGING THE CAUSE OF THE INITIATION OF A VOLTAGEBREADOWN ARC IN SAID TRANSMISSION LINE CIRCUIT BY CONTINUALLY DISABLINGAND ENABLING SAID ENERGY SOURCE UNTIL SAID CAUSE IS REMOVED.